Defrosting control for refrigerating apparatus



Oct. 22, 1963 C. A. STICKEL DEFROSTING CONTROL FOR REFRIGERATING APPARATUS Filed June '16. 1961 IN VEN TOR. lg- 3 Carl A. Slicke/ United States Patent Office 3,107,501 Patented Oct. 22, 1963 3,107,501 DEFROSTENG CONTROL FOR REFRIGERATING APPARATUS Carl A. Stickel, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporationof Delaware Filed lune 16, 1961, Ser. N. 117,741 6 Claims. (Cl. 62-156) This invention pertains to refrigerating apparatus and more particularly to defrost controls operated only at prolonged periods.

Defrosting controls operating only at prolonged periods are efficient and practical. However, the clock mechanisms normally used to time such periods are subject to frequent contact failures, mechanical failures and electrical failures in addition to using electrical energy. Since the clock motor operates continuously, there is much wear and often continuous noise after a comparatively short period of operation.

It is an object of this invention to provide a simple reliable, efiicient, quiet defrost control which operates only at prolonged periods and which can be manufactured without resort to critical limits.

It is another object of this invention to provide a simple, reliable, eflicient, quiet defrost control in which the mechanism does not operate except at prolonged periods of about once a day.

It is another object of this invention to employ the slow freezing and expansion of an aqueous liquid within an insulated elongated tube cooled at one end by the evaporator for controlling the timing of the defrosting periods. These and other objects are attained in the forms shown in the drawings in which the bellows and the major portions of a long capillary tube connected thereto are located in a portion of the refrigerator which is normally above freezing and which has an end portion located in contact with the evaporator. This tube and bellows contains a freezing solution, such as water or water and normal butyl alcohol, which will, during normal operation, progressively freeze from the evaporator toward the bellows. At the end of a prolonged period, such as about twentyfour hours, the bellows will be actuated to operate a double throw switch disconnecting the motor compressor unit and fan from the electrical supply and connecting a defrost heater or other defrost means to the electrical supply for heating the evaporator. A second heater is provided for the capillary tube. In a first form, this second heater is energized by an evaporator thermostat only at the end of the defrost period. This heater and capillary tube may be enclosed within a flexible plastic tube having heat insulating and electrical insulating properties. In a second form, this second heater is energized during the defrost period and is arranged so that it terminates the defrost period at the time that the defrosting of the evaporator is completed.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a side sectional view through a refrigerator embodying one form of my invention;

FIGURE 2 is a wiring diagram for the refrigerator shown in FIGURE 1;

FIGURE 3 is a modified wiring diagram; and

FIGURE 4 is a transverse sectional view through the capillary defrost control tube, the electric heater and the surrounding plastic tube.

Referring now to the drawings, there is shown an insulated refrigerator cabinet 20 having insulated upright and horizontal walls enclosing an upper freezing compartment 22 and a lower above freezing compartment 24. The upper below freezing compartment 22 is provided with a false bottom wall 26 beneath which there is provided an evaporator compartment 28 having entrances at the front. One of the entrances 30 provides an inlet for air from the below freezing compartment while a second entrance 32 extends through the insulated horizontal wall 34 dividing the below freezing compartment 22 from the above freezing compartment 24. This entrance or passage 32 through the wall 34 conducts the air from the above freezing compartment into the front of the evaporator compartment 28. The evaporator eompartment 23 contains a fin and tube evaporator 36.

At the rear of the evaporator compartment 28 is a centrifugal fan 38 driven by an electric motor 40 and having an upwardly extending discharge outlet 42 extending to the top of the below freezing compartment 22 and discharging therein for keeping the compartment 22 at below freezing temperatures. The fan 38 alsohas a downwardly extending discharge outlet 44 for discharging a reduced volume of cold air into the above freezing compartment 24. The volume of air discharged through the outlet 44 is sufficiently reduced to keep the compartment 24 at above freezing refrigeration temperature. In the bottompf the cabinet 20 there is provided a sealed motor compressor unit 46 for withdrawing evaporated refrigerant from the evaporator 36 through the suction conduit 48 and for discharging compressed refrigerant into the condenser 59 where the refrigerant condenses and is forwarded under the control of a flow regulating device 52 through the supply conduit 54 to the evaporator 36.

Because of the opening of the doors 56 and 5S and the deposit of packages containing moisture in the compartments 22 and 24, this circulating air gradually carries moisture to the surfaces of the evaporator 36 on which the moisture deposits in the form of frost. Heretofore, it has been customary to resort to clock timers for defrosting the evaporator 36 about once a day. Since these clock timers operate continuously, there is much wear.

Often these clock timer mechanisms develop considerable noise after a comparatively short period of operation. More often, the clock timer becomes noisy before the end of the useful life of the refrigerator. Because of its continuous operation, it is necessary to keep the current consumption for the clock timer at a minimum. This entails mechanical devices incorporating a mechanism to store energy for operating the contacts or switch mechanism. This mechanism is subject to frequent failure and also to contact failure.

It is therefore an object of this invention to provide a simple powerful mechanism which will operate the defrost switch only about once a day and be idle at all other periods. This is accomplished by providing a long capillary tube 60 having one end thereof mounted upon the return bend 62 of the refrigerant tubing of the evaporator 36. The remainder of the capillary tube 60 extends through the warm lower portion of the horizontal insulated wall 34 located between the compartments 22 and r 24. This remaining portion of the capillary tube 60 is maintained at above freezing temperatures by the above freezing temperature of the above freezing compartment 24 beneath it. The opposite end of the capillary tube-60 is connected to a fluid motor 64 in the form of a flexible metal bellows. motor 64 are completely filled with a freezing liquid, such as water or a freezing solution which does not completely solidify such as water and 5% by weight of diethylene glycol monobutyl ether commonly known as butyl carbitol or 10% by weight of normal butyl alcohol As shown in the wiring diagram in FIGURE 2, the fluid motor 64 is The capillary tube 60 and the fluid 43 connected through a primary lever 66 and a U-shaped toggle spring 68 to a double throw switch member 70 connected to the supply conductor 72. This double throw switch member 70 is normally held in engagement with the stationary contact 74 by the primary lever 66 and the toggle spring 68. The fluid motor 64 and the primary lever 66 are continuously loaded by the return spring 67. This contact 74 is connected through the conductor 76 and the thermostat switch 78 to the sealed unit 46 which in turn is connected to the second supply conductor 80. The fan motor 40 is connected in parallel with the sealed unit 46 and operates simultaneously with it.

The thermostatic switch 78 is operated by a fluid motor 82 connected to a capillary tube 84 having its end portion located in the rear of the evaporator compartment 28 so it is responsive to the air after being cooled by the evaporator 36. The switch through the vapor charge of the fluid motor bellows 82 and the capillary tube 84 is opened and closed in accordance with temperatures of the rear of the evaporator compartment to keep the evaporator 36 as well as the below and above freezing compartments 22 and 24 at desirable below freezing and above freezing temperatures. As the frost gradually accumulates on the evaporator and begins to obstruct the flow of air through the evaporator compartment 28, the freezing solution within the capillary tube 60 progressively freezes and gradually expands with adequate power the bellows or fluid motor 64 until at the end of approximately twentyfour hours the toggle spring 68 will trip to move the double throw switch 70 away from the contact 74 to stop the operation of the sealed unit 46 and the fan motor 40 and into contact with the opposite contact 86 to start the defrosting period.

The contact 86 connects through the conductor 83 to the defrost heater 90 which in turn is connected through the conductor 92 with the second supply conductor 30. The defrost heater 90 is of the sheathed tubular type and extends in serpentine fashion through notches provided in the upper and lower edges of the tins of the evaporator 36. The defrost heater 90 continues to heat the evaporator 36 while the fan motor 40 and the sealed unit 46 are idle. When the host is removed from the evaporator 36, its temperature rises. This is detected by a normally open defrost limiter switch 94 which closes at some suitable temperature indicating the completion of the defrosting, such as 37 F. This thermostatic switch 94 is preferably of bimetal type. It is connected in series with a small low wattage heater 96 connected in parallel with the defrost heater 99. This small heater 96 is wrapped around the capillary tube 60 and heats the capillary tube 60 at the end of the defrost period to melt and thereby contract the ice and frozen liquid within the capillary tube 60 so as to return the defrost switch 70 to the position shown in FIGURE 2 by the contraction of the fluid motor 64 with the assistance of the return spring 67. As shown in FIGURE 4, the capillary tube 60 and the heater 96 are preferably enclosed in an electrical and heat insulating plastic tube 98 which confines the heat produced by the heater 96 to the capillary tube 60 and prevents or minimizes the effect of environment temperature upon the capillary tube 60.

The wiring diagram shown in FIGURE 3 is similar to that shown in FIGURE 2 with the exception that the defrost limiter switch 94 is omitted and the heating rate and Wattage of the heater Q6 is considerably reduced. It is energized during the entire defrost period and has only sufficient heat to heat the capillary tube to accomplish the melting and consequent contraction of the freezing liquid in the capillary tube shortly after the completion of the defrosting of the evaporator 36 by the heater 90. This heating is assisted by the heat transmitted from the heater 0 through the evaporator 36 to the end of the capillary tube 60 mounted upon the end turn 62 of the refrigerant tubing.

In either of these forms, there is no mechanism operating during the normal operation of the system. The double throw switch is not operated until the start of the defrost period. The switch 70 is returned to normal position at the end of the defrost period. Since this mechanism only operates about once every twenty-four hours, there is little wear and little possibility of failure. The simple switch mechanism makes very little noise and there is no other mechanism operating to provide any other noise. The frequency of the defrost periods may be varied by varying the length of the capillary tube 60. This may also be varied by introducing various amounts of anti-freeze into the freezing solution. The mechanism is simple, inexpensive and reliable.

While the embodiments of the present invention, as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. Refrigerating apparatus including an evaporator, refrigerant liquefying means operatively connected to said evaporator, control means for controlling said liquefying means for normally maintaining said evaporator at below freezing temperatures, a defrosting control having a normal position for normal refrigeration by said liquefying means under the control of said control means for maintaining said evaporator at below freezing temperatures and having a defrosting position, said defrosting control comprising a long small diameter closed tube having one portion in heat transfer relation with the evaporator and a second portion remote and isolated from the first portion provided with an expansible chamber fluid motor having means for determining the normal position and the defrost position, said tube and fluid motor containing a freezing liquid having a freezing point above the lowest temperature of said evaporator and having the property of expanding upon freezing for operating said expansible chamber fluid motor upon the progressive freezing of said liquid through a sufficient length of the tube to set the defrosting control in the defrost position and for operating said fluid motor upon the retrog'ression of the freezing of said liquid through a sufiicient length of the tube to set the defrosting control in the normal position, and means responsive to the setting of said control in the defrost position for defrosting said evaporating means and heating said closed tube until the freezing liquid thaws in a sufficient length of the tube to return the defrosting control to normal position.

2. Refrigerating apparatus including an evaporator, electrically operated refrigerant liquefying means operatively connected to said evaporator, thermostatic cycling switch means connected in series circuit with said electrically operated liquefying means for normally maintaining said evaporator at below freezing temperatures, a defrosting control comprising first contact connected in series with said cycling switch means and said liquefying means and a second contact, said defrosting control also comprising a long small diameter closed tube having one portion in heat transfer relation with the evaporator and a second portion remote from the first portion provided with an expansible chamber fiuid motor and a switch de vice operated by said fluid motor to energize alternately said first and second contacts, an electrically operated defrosting means for defrosting and coincidentally heating said evaporator electrically connected in series with said second contact, said tube and fluid motor containing a freezing liquid having a freezing point above the lowest temperature of said evaporator and having the property of expanding upon freezing for operating said expansible chamber fluid motor upon the progressive freezing of the liquid through a sufficient length of the tube to move the defrosting control into energizing relation with said second contact to initiate the defrosting of said evaporator and during said defrosting for operating said fluid motor upon the consequential heating and retrogression of the freezing of said liquid through a sufficient length of the tube to move the defrosting control into energizing relation with said first contact.

3. Refrigerating apparatus including an evaporator, electrically operated refrigerant liquefying means operatively connected to said evaporator, thermostatic cycling switch means connected in series circuit with said electrically operated liquefying means for normally maintaining said evaporator at below freezing temperatures, a defrosting control comprising first contact connected in series with said cycling switch means and said liquefying means and a second contact, said defrosting control also comprising along small diameter closed tube having one portion in heat transfer relation with the evaporator and a second portion remote from the first portion provided with an expansible chamber fluid motor and a switch device operated by said fluid motor to energize alternately said first and second contacts, an electrically operated defrosting means for defrosting said evaporator electrically connected in series with said second contact, an electric heater associated with said tube and connected in series with said second contact, said tube and fluid motor containing a freezing liquid having a freezing point above the lowest temperature of said evaporator and having the property of expanding upon freezing for operating said expansible chamber fluid motor upon the progressive freezing of the liquid through a suflicient length of the tube to move the defrosting control into energizing relation with said second contact and for operating said fluid motor upon the thawing of said liquid in a suificient length of the tube to move the defrosting control into energizing relation with said first contact.

4. Refrigerating apparatus including an evaporator, electrically operated refrigerant liquefying means operatively connected to said evaporator, thermostatic cycling switch means connected in series circuit with said electrically operated liquefying means for normally maintaining said evaporator at below freezing temperatures, a defrosting control comprising first contact connected in series with said cycling switch means and said liquefying means and a second contact, said defrosting control also comprising a long small diameter closed tube having one portion in heat transfer relation with the evaporator and a second portion remote from the first portion provided with an expansible chamber fluid motor and a switch device operated by said fluid motor to energize alternately said first and second contacts, an electrically operated defrosting means for defrosting said evaporator electrically connected in series with said second contact, an electric heater associated with said tube and connected in series with said second contact, said tube and fluid motor containing a freezing liquid having a freezing point above the lowest temperature of said evaporator and having the property of expanding upon freezing for operating said expansible chamber fluid motor upon the progressive freezing of the liquid through a suflicient length of the tube to move the defrosting control into energizing relation with said second contact and for operating said fluid motor upon the thawing of said liquid in a suflicient length of the tube to move the defrosting control into energizing relation with said first contact, and a normally open defrost limiter switch mounted upon said evaporator and connected in series with said heater and in parallel with said defrosting means for controlling the end of the defrosting.

5. Refrigerating apparatus including an evaporator, electrically operated refrigerant liquefying means operatively connected to said evaporator, thermostatic cycling switch means connected in series circuit with said electrically operated liquefying means for normally maintaining said evaporator at below freezing temperatures, a defrosting control comprising first contact connected for defrosting said evaporator electrically connected in series with said second contact, an electric heater associated with said tube and connected in series with said second contact, said tube and fluid motor containing a freezing liquid having a freezing point above the lowest temperature of said evaporator for operating said fluid motor upon the progressive freezing of the liquid through a suflicient length of the tube to move the defrosting control into energizing relation with said second contact and for operating said fluid motor upon the thawing of said liquid in a suflicient length of the tube to move the defrosting control into energizing relation with said first contact, and a tube of electrical and heat insulating mate-rial surrounding said electric heater and a major portion of said small diameter closed tube for assisting in confining of the heat of said heater to said small tube and reducing the effect of the temperature of the environment thereon.

6. Refrigerating apparatus including an evaporator, refrigerant liquefying means operatively connected to said evaporator, control means for controlling said lique- -fying means for normally maintaining said evaporator at below freezing temperatures, a defrosting control having a normal position for normal refrigeration by said liquefying means under the control of said control means for maintaining said evaporator at below freezing temperatures and having a defrosting position, said defrosting control comprising a long small diameter closed tube having one portion in heat transfer relation with the evaporator and a second portion remote and isolated from the first portion provided with an expansible chamber diaphragm means and means responsive to the deflection of said diaphragm means in response to the expansion of said chamber for moving said defrosting control from the normal position to the defrost position and responsive to the deflection of said diaphragm means in response to the contraction of said chamber for moving said defrosting control from the defrost position to the normal position, said tube and expansible chamber diaphragm means containing a freezing liquid having a freezing point above the lowest temperature of said evaporator and having the property of expanding upon freezing for operating said expansible chamber diaphragm means upon the progressive freezing of said liquid through a sufiicient length of the tube to set the defrosting control in the defrost position and for operating said eX-pansible chamber diaphragm means upon the retrogression of the freezing of said liquid through a suflicient length of the tube to set the defrosting control in the normal position, and means responsive to the setting of said control in the defrost position for defrosting said evaporating means and heating said closed tube until the freezing liquid thaws in a sufiicient length of the tube to return the defrosting control to normal position.

References Cited in the file of this patent UNITED STATES PATENTS 3,013,399 Simmons Dec. 19, 1961 3,023,589 Jacobs Mar. 6, 1962 

1. REFRIGERATING APPARATUS INCLUDING AN EVAPORATOR, REFRIGERANT LIQUEFYING MEANS OPERATIVELY CONNECTED TO SAID EVAPORATOR, CONTROL MEANS FOR CONTROLLING SAID LIQUEFYING MEANS FOR NORMALLY MAINTAINING SAID EVAPORATOR AT BELOW FREEZING TEMPERATURES, A DEFROSTING CONTROL HAVING A NORMAL POSITION FOR NORMAL REFRIGERATION BY SAID LIQUEFYING MEANS UNDER THE CONTROL OF SAID CONTROL MEANS FOR MAINTAINING SAID EVAPORATOR AT BELOW FREEZING TEMPERATURES AND HAVING A DEFROSTING POSITION, SAID FROSTING CONTROL COMPRISING A LONG SMALL DIAMETER CLOSED TUBE HAVING ONE PORTION IN HEAT TRANSFER RELATION WITH THE EVAPORATOR AND A SECOND PORTION REMOTE AND ISOLATED FROM THE FIRST PORTION PROVIDED WITH AN EXPANSIBLE CHAMBER FLUID MOTOR HAVING MEANS FOR DETERMINING THE NORMAL POSITION AND THE DEFROST POSITION, SAID TUBE AND FLUID MOTOR CONTAINING A FREEZING LIQUID HAVING A FREEZING POINT ABOVE THE LOWEST TEMPERATURE OF SAID EVAPORATOR AND HAVING THE PROPERTY OF EXPANDING UPON FREEZING FOR OPERATING SAID EXPANSIBLE CHANBER FLUID MOTOR UPON THE PROGRESSIVE FREEZING OF SAID LIQUID THROUGH A SUFFICIENT LENGTH OF THE TUBE TO SET THE DEFROSTING CONTROL IN THE DEFROST POSITION AND FOR OPERATING SAID FLUID MOTOR UPON THE RETROGRESSION OF THE FREEZING OF SAID LIQUID THROUGH A SUFFICIENT LENGTH OF THE TUBE TO SET THE DEFROSTING CONTROL IN THE NORMAL POSITION, AND MEANS RESPONSIVE TO THE SETTING OF SAID CONTROL IN THE DEFROST POSITION FOR DEFROSTING SAID EVAPORATING MEANS AND HEATING SAID CLOSED TUBE UNTIL THE FREEZING LIQUID THAWS IN A SUFFICIENT LENGTH OF THE TUBE TO RETURN THE DEFROSTING CONTROL TO NORMAL POSITION. 